title: Identification of the pH-dependent membrane anchor of carboxypeptidase E (EC 3.4.17.10).
abstract: Carboxypeptidase E (CPE), a peptide hormone-processing enzyme, is present within secretory granules in both a soluble form and a form which is membrane-bound at pH 5.5 but soluble at neutral pH. Antisera raised against a peptide corresponding to the predicted COOH-terminus of CPE bind to the membrane-associated form of CPE but not to the soluble form. This COOH-terminal region is predicted to form an amphiphilic alpha-helix, containing several pairs of hydrophobic residues separated by hydrophilic residues. Synthetic COOH-terminal peptides 11-24 residues in length are able to bind to bovine pituitary membranes and can be extracted by conditions that extract the membrane-bound form of CPE. The influence of pH on the membrane binding of a 21-residue COOH-terminal peptide is similar to the membrane binding of CPE: at pH values less than 6 the majority of the peptide is membrane-bound, while at pH values above 8 less than 20% is membrane-bound. Both the 21-residue COOH-terminal peptide and the purified membrane form of CPE, but not the soluble form, partition into Triton X-114 only at low pH (pH less than 6). Combined polar and hydrophobic interactions of the COOH-terminal peptide appear to be responsible for the reversible, pH-dependent association of CPE with membranes.
authors.affiliation: Department of Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, New York 10461.
authors.forename: L D
authors.initials: LD
authors.lastname: Fricker
authors.forename: B
authors.initials: B
authors.lastname: Das
authors.forename: R H
authors.initials: RH
authors.lastname: Angeletti
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D043423:Carboxypeptidase H; D002268:Carboxypeptidases / Q000235:genetics / Q000378:metabolism*; D002417:Cattle; D002462:Cell Membrane / Q000201:enzymology; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008969:Molecular Sequence Data; D010455:Peptides / Q000138:chemical synthesis / Q000378:metabolism; D010902:Pituitary Gland / Q000201:enzymology*; D011485:Protein Binding; D011487:Protein Conformation; D051381:Rats
chemical_list: D010455:Peptides; D002268:Carboxypeptidases; D043423:Carboxypeptidase H